Zeolite is in use as catalyst, catalyst carrier, adsorbent material, etc. Also, a zeolite membrane is comprised of a porous substrate made of a metal or a ceramic and a zeolite membrane formed thereon, and has come to be used as a gas separation membrane or a pervaporation membrane, by utilizing the molecular sieve function of zeolite.
Zeolites are classified such as LTA, MFI, MOR, AFI, FER, FAU, DDR and the like according to their crystal structures. Of these, DDR (Deca-Dodecasil 3R) is a crystal whose main component is silica and has pores formed by a polyhedron containing an oxygen eight-membered ring. The pore diameter of the oxygen eight-membered ring is 4.4×3.6 angstroms [see W. M. Meier, D. H. Olson, Ch. Baerlocher, Atlas of zeolite structure types, Elsevier (1996)].
Of various zeolites, DDR type zeolite has relatively small pores and can be used as a molecular sieve membrane to low-molecular weight gases such as carbon dioxide (CO2), methane (CH4), ethane (C2H6) and the like.
With respect to the method for production of DDR type zeolite, there is disclosed, for example, a method for producing a DDR type zeolite, which comprises immersing a DDR type zeolite seed crystal in a raw material solution containing 1-adamantaneamine, silica, water and ethylenediamine and conducting a hydrothermal synthesis to give rise to crystal growth in a short time. In this method, it is also possible to produce a dense DDR type zeolite membrane on a porous substrate (see Patent Literatures 1 and 2).
In conventional known production methods including the methods described in the Patent Literatures 1 and 2, the DDR type zeolite membrane after formation by hydrothermal synthesis has a form in which the 1-adamataneamine used as a structure-directing agent is taken into the pores of DDR zeolite. Therefore, in these methods for producing a DDR type zeolite membrane, there is required a step of heating the DDR type zeolite membrane, just after formation by hydrothermal synthesis, in order to burn and remove the 1-adamantaneamine.    Patent Literature 1: JP-A-2004-66188    Patent Literature 2: JP-A-2004-83375
However, when the DDR type zeolite membrane is heated in order to burn and remove the 1-adamantaneamine, cracks are generated easily in the DDR zeolite membrane at a high frequency, due to the difference in thermal expansion between the porous substrate and the DDR zeolite membrane formed thereon. There is a means of burning and removing the 1-adamantaneamine at a lower heating temperature. However, with a lower heating temperature, the 1-adamantaneamine remains in the DDR type zeolite membrane. The generation of cracks in DDR type zeolite membrane and the remaining of 1-adamantanamine in DDR type zeolite membrane invite a reduction in separation ability of DDR type zeolite membrane to low-molecular weight gas, etc. However, in conventional known methods for producing a DDR type zeolite membrane, the above-mentioned problems of crack generation and 1-adamantaneamine remaining, which invite a reduction in separation ability of DDR type zeolite membrane, are undissolved yet.